1. Field of the Invention
The present invention generally relates to latex drag reducers comprising high molecular weight polymers produced according to an emulsion polymerization reaction and methods of using the same.
2. Description of the Prior Art
A drag reducer is a composition capable of substantially reducing friction loss associated with the turbulent flow of a fluid through a conduit. Where fluids are transported over long distances, such as in oil and other hydrocarbon liquid pipelines, these friction losses result in inefficiencies that increase equipment and operations costs. Ultra-high molecular weight polymers are known to function well as drag reducers, particularly in hydrocarbon liquids. In general, drag reduction depends in part upon the molecular weight of the polymer additive and its ability to dissolve in the hydrocarbon under turbulent flow. Effective drag-reducing polymers typically have molecular weights in excess of five million.
In the past, it has been proposed that drag reducers comprising polymeric latex emulsions can be used to reduce friction loss associated with turbulent fluid flow through a conduit. The use of polymeric latex emulsion drag reducers has most commonly been proposed for application to the flow of hydrocarbon streams (e.g., crude oil, gasoline, diesel fuel, etc.) through pipelines. In order to be most effective, the drag reducer must be dissolved in the hydrocarbon stream. However, in many instances, great difficulty has been encountered in dissolving the polymeric material contained in the latex emulsion into the hydrocarbon stream.
Previous proposals for solving the dissolution problem associated with polymeric latex emulsions have involved the addition of large amounts of lower aliphatic alcohols to the hydrocarbon stream prior to the addition of the latex emulsion in order to promote dissolution of the polymer. This two-step process is generally referred to as a “pre-activation” technique. Other attempts have been proposed to lessen this problem by premixing the latex emulsion with a solution of hydrocarbon and alcohol to “break” the emulsion prior to adding pre-solvated polymer to a hydrocarbon stream. These methods can prove rather costly as they require purchasing significant quantities of alcohol or other polar additives and also necessitate additional storage and mixing equipment. As a result of this and other difficulties associated with past proposals for polymeric latex emulsion drag reduces, this type of drag reducer has never been a commercially viable option to conventional drag reducers.
Current commercial methods include drag reducing polymers in bulk. These polymers must react for periods as long as 21 days in order to achieve the desired molecular weight. The reacted polymer must then be compounded with a partitioning agent, milled to less than 800 microns under cryogenic conditions, and prepared into a high solids suspension. Suspensions prepared in this manner have a tendency to separate when stored in the field locations prior to injection. Special equipment is needed to maintain the suspensions to avoid separation. This equipment typically includes provisions for agitation and protection from excessive heat.
Currently, a number of different commercial approaches are being taken to address the problem of preparing, dissolving, transporting and using such drag reducing polymers. In use, the polymers form extremely dilute solutions ranging from about 1 up to about 100 parts per million polymer and hydrocarbon, yet remain effective in order to receive drag reduction or anti-misting. A common commercial method is to prepare the polymer in dilute solutions in an inert solvent such as kerosene or other solvating material. This method utilizes a solution of high molecular weight polymer suitable for use as a drag reducing agent when produced by polymerization of alpha olefins in a hydrocarbon solvent. The entire mixture, containing polyolefin, solvent, and catalyst particles is used without separation to form dilute solutions of the polymer in crude oil or finished hydrocarbons. However, one disadvantage of such approach is the use of a solvent which poses a shipping and handling difficulty and may constitute a hazard. In addition, the product itself forms a gel-like substance which is difficult to introduce into flowing hydrocarbon streams and which becomes extremely viscous and difficult to handle under cold temperature conditions, particularly when injection into conduits at remote locations is required.
Accordingly, there exists a need for an improved, stable, single-step, latex drag reducer that can be directly added to the hydrocarbon fluid and provide satisfactory drag reduction without the need to pre-activate or pre-dissolve the polymer in a mixture of alcohol or another polar molecule.